"Yes, we found water," said Anthony Colaprete, the principal investigator for NASA's Lunar Crater Observation and Sensing Satellite (LCROSS), a mission that culminated in a spectacular crash on the surface of the moon about a month ago. (See a guide to the 40th anniversary of the moon landing.)

For years, scientists have been tantalized by the prospect that water ice lurks in craters near the poles of the moon, places where the sun never shines and temperatures perpetually hover hundreds of degrees below zero. A decade ago, the Lunar Prospector orbiter caught a whiff of hydrogen, which may or may not have been evidence of that ice.

Now, thanks to LCROSS, the verdict is finally in. Not only does water exist on the moon, but it has been uncovered by the bucketful  about 24 gallons' worth. It was the intentional crash of the mission  in two separate stages  on Oct. 9 that made the discovery possible. The first piece of LCROSS slammed into the floor of a crater called Cabeus, some 60 miles from the moon's south pole, excavating a hole more than 60 ft. across and sending up a plume of pulverized material about 6 miles wide. Then, about four minutes later, the second part of the craft smashed down  but not before its instruments analyzed the dust cloud to see what it was made of. (See the top 10 things you didn't know about the moon.)

At the time, viewers from Earth were disappointed. They had been told  incorrectly, as it turned out  that they would be able see the impact through large amateur telescopes. Reporters were frustrated because, despite the drama, no actual information was available right away. It took a month of what Colaprete calls 28-hour days to extract the major news that there is, in fact, water on the moon.

But the discovery was worth the wait. Analysis of the water ice may give scientists an eons-long look at environmental history: any ice lurking in the shadows of lunar craters would have been there for a long, long time  billions of years, even. On Earth, for example, scientists get their best information about the planet's climatic history from ancient air trapped in polar ice, says Greg Delory of the Space Sciences Laboratory at the University of California, Berkeley. Similarly, the lunar poles are record keepers of conditions over long periods. They are the dusty attic of the solar system, says Michael Wargo, chief lunar scientist at NASA headquarters.

The moon's ice might have come from comet impacts, which would date it back to the earliest days of our solar system; that ice would hold a record of the cosmic chemistry of those formative times. But the ice could have also been formed by particles streaming from the sun, which gradually combined with lunar minerals to form water, then ice. Or it might have come from Earth, perhaps in the gigantic collision that created the moon in the first place. Whatever its origins, says Delory, the prospect of studying it is really exciting.

In addition to its historical significance, water on the moon holds prospects for the future. If humans are ever going to establish a long-term presence on the moon, they will need water to drink, and tapping a local supply would be a lot more convenient than lugging it from Earth. Beyond that, water can be split into hydrogen and oxygen  the former makes pretty good rocket fuel, and the latter is useful for breathing.

LCROSS scientists still have to figure out how thinly the water ice is spread in the lunar rock and soil and how deeply it's buried. That analysis is pending, and so is the full report on all the other material that was blasted into the air on impact. Stay tuned, says NASA's Wargo. There are plenty of updates to come.